The recovery of copper from scrap copper wire and cable is of active interest in the telephone, cable and power industries. Generally, the scrapped wire or cable is first chopped into small pieces by a standard commercially available chopping machine, then the chopped copper wire or cable is placed on an air gravity table to separate the heavy material such as copper and other metals from the plastic insulating jacket, paper and fibrous materials. Thereafter, the recovered copper is refined by any one of the known copper refining techniques. In most instances, the preliminary separation of copper from the contaminants such as plastics, textiles, paper, and other metals is not complete. In order to enhance the efficiency of the final refining process it is preferable to further separate from the chopped copper those residual contaminants that are mixed therewith or lie on the surface of the copper.
In the past, a number of methods have been used to treat copper for the removal of certain contaminants. For example, U.S. Pat. No. 155,368 describes a method by which tin may be removed from the surface of copper shells by boiling the shells in an aqueous solution of calcium chloride. U.S. Pat. No. 3,762,911 describes the removal of lead, tin and zinc from the surface of high melting metal alloys such as copper-nickel alloy by heating the alloy in a vacuum so as to vaporize the impurities from the surface thereof. In U.S. Pat. No. 3,853,543 there is described a method for processing copper-bearing materials, such as copper scrap or ore, by first reacting the copper scrap or ore with a ferric chloride leaching agent to convert the copper to cuprous chloride, separating the cuprous chloride from the ferric chloride mixed therewith and then melting the cuprous chloride in the presence of zinc at 1100.degree. C. to produce vaporized zinc chloride and molten copper. In U.S. Pat. No. 121,948, there is described a method of removing tin from the surface of tin plated metals such as iron or copper which involves treating the metal with a solution of caustic soda or potash. In U.S. Pat. No. 3,866,893 there is described an apparatus and method for desoldering scrap radiator cores and recovering separated metals. Here, the solder from the radiator cores is removed by means of a fused salt bath at temperatures of about 700.degree. to 775.degree. F. whereby the solder is sweated out of the radiator cores. This patent teaches that suitable fused salt baths comprise alkali metal salts such as fused sodium nitrate with a small amount (up to 1%) of sodium dichromate or a 50/50 mixture of sodium nitrate and potassium nitrate with the addition of small amounts of potassium chromate. While this method is suitable for removing many of the contaminants from the surface of copper scrap, the salt baths suggested in U.S. Pat. No. 3,866,893 do not adequately remove certain contaminants such as tin from the copper surface.